Book reviews

Dr Ron Close in his presidential address (A.P.P. 7 (2): 17 -20. 1978) provided a thoughtful discussion of the concept of Plant Pathology in which he mentioned the "plant disease triangle" and its evolution to a square and then to a pyramid by the addition of time and man. These are important additions to the original concept and I have begun to include them in my own teaching of Plant Pathology. I present the relationships somewhat differently to Dr Close as is shown in figure 1. In this figure the triangular pyramid represents the interrelationship of the four main disease components host, pathogen, environment and time; the sphere represents man's ability to influence each of the components. In my opinion man should not be considered an integral part of the plant disease pyramid because diseases do exist in the absence of man. One must of course recognize that in modern agriculture (horticulture, forestry, etc.) man has the capacity to influence all four components and frequently does.